Pulper tank

ABSTRACT

A pulper tank structure wherein a horizontal bottom wall associated with a rotor is connected to a vertically extending cylindrical sidewall thereabove and interconnected by at least two upwardly divergent intermediate frusto-conical walls and where the fillet angles are specified for advantageously increasing stock surface rate or reducing power consumption.

United States Patent [191 Honeyman et al.

[ PULPER TANK [75] Inventors: Robert Blakeley Honeyman, Carmel,

Calif.; Robert Lee Crawford, Portland, Oreg.

[73] Assignee: Morden Machines Company,

Portland, Oreg.

[22] Filed: June 20, 1973 [21] Appl. N0.: 371,745

[52] US. Cl. 24l/46.l7 [51] Int. Cl. B04c 5/081 [58] Field of Search241/46 R, 46.02, 46.04,

[56] References Cited UNITED STATES PATENTS 2,345,474 3/1944 Haverland24l/46.06 X

[111 3,874,600 Apr. 1, 1975 3,009,656 11/1961 Martindale 24l/46.173,085,756 4/1963 Danforth et al. 241/46.l7 X 3,310,243 3/1967 Duncan etal. 241/46.17 X

Primary Examiner-Roy Lake Assistant Examiner-Craig R. Feinberg Attorney,Agent, or Firm-Dawson, Tilton, Fallon & Lungmus [57] ABSTRACT A pulpertank structure wherein a horizontal bottom wall associated with a rotoris connected to a verti cally extending cylindrical sidewall thereaboveand interconnected by at least two upwardly divergent intermediatefrusto-conical walls and where the fillet angles are specified foradvantageously increasing stock surface rate or reducing powerconsumption.

1 Claim, 2 Drawing Figures PATENTEBAPR 1197s FIG. I

FIG.2

I) D Wm PULPER TANK BACKGROUND AND SUMMARY for defiberizing paper makingmaterial and extracting refined pulp therefrom.

The major considerations in the design of a pulper tank are installedcost, space requirement (diameter and height), maximum circulation forapplied power and service ability. The important factors influencing thecirculation pattern are the bottom configuration and thediameter-to-height ratio. We are concerned here only with the former.

The stock (at 4-77c consistency) discharges from the rotor blades orvanes at a given velocity and resultant angle caused by the combinedcentrifugal reaction, the blade angle, and the peripheral speed of therotor. The resultant flow is normally angular, not radial, causing acircular motion of the body of stock or water in the tank. Excessiverotational circulation will cause the stock and/or water to rise up thewall of the tank to an uncontrollable level and can create an excessiveprerotation effect causing an open vortex above the rotor, allowingextensive air entrainment and general deterioration of the pulpingcycle. Excessive rotation is prevented or controlled by the well-knownpractice of placing stationary baffles or deflectory on the bottom orsidewalls of the tank. Because the pulper, even when being operatedcontinuously, is essentially a closed system, the effect of thedischarge flow from the impeller creates a suction in the eye of therotor. In turn, this results in a rapid flow of material back into theworking zone of the rotor for repeated difibering action. The returnflow can best be measured on the surface of the tank by simple means andrelated to the efficiency of defibering on the basis ofhorsepower/day/ton of stock. Ideally, the surface flow or circulationrate will be rapid but not excessive and will rotate sufficiently tocause a vigorous but closed vortex to aid in the submergency of anymaterial additions.

The velocity of flow of material decreases rapidly after leaving theblade area due to friction and dispersion. Any abrupt change indirection, particularly in the high velocity areas, causes turbulenceand internal friction in the mass of material even though the tank wallsare smooth and provide little surface friction. We have determined thatto avoid abrupt angular changes in flow, an ideal tank bottomconfiguration would be elliptical in cross section with the rotorcentered on the short axis. Cost prevents practical consideration ofthis approach, particularly for fabricated construction. We havedetermined therefore that optimum results are obtained when thegenerally horizontal bottom wall is joined to the much larger diametercylindrical sidewall by at least two upwardly divergent, generallyfrustoconical walls, one above the other, and with the fillet anglesbeing defined as follows. The lower of the frustoconical walls forms afirst exterior angle of at least about but not more than about 30 withthe horizontal. A second exterior angle is that between the upper andlower frusto-conical walls and is equal to or greater than the firstangle. A third exterior angle is that between the upper frusto-conicalsidewall and is equal to or greater than the second mentioned angle andwith all of the angles being not more than about 40.

DETAILED DESCRIPTION The invention is described in conjunction with theaccompanying drawing, in which FIG. 1 is a fragmentary side elevationalview of a tank constructed according to teachings of this invention; and

FIG. 2 is a reduced scale version of the tank seen in FIG. 1 and withcertain lettering applied thereto relating to fillet angles.

Referring now to FIG. 1 the numeral 10 designates generally a pulpertank which is seen to include in the central bottom a rotor generallydesignated 11 equipped with a plurality of laterally extending vanes orblades. As will be brought out in the test description givenhereinafter, we have worked with types of rotors,

one of which is described in U.S. Pat. No. 2,858,990

and the other in my copending application Ser. No. 330,081 filed Feb. 6,1973. The invention provides advantages with both types of rotors.

Still referring to FIG. 1, the numeral 13 designates a generallycylindrical, upwardly extending sidewall which is connected to thebottom wall 14 by at least two intermediate, upwardly divergent,generally frustoconical walls as at 15 and 16. The level of stock isdesignated 17 providing an axial vortex at 18 while the dotted linedesignated 19 shows the stationary or static level of the stock in thetank 10.

In FIG. 2, we have shown a schematic representation of a pulper tank andhave applied certain symbols to refer to various fillet angles. Thesymbols, A, B and C are exterior fillet angles and are those referred tohereinbefore. For example, the fillet angle A is defined between thelower frusto-conical wall and the horizontal. The second fillet angle Bis included between the exterior of the upper frusto-conical wall andthe extension of the lower frusto-conical wall. The third exterior angleC is defined between the exterior of the generally cylindrical sidewalland the extension of the upper generally frusto-conical wall. Forconvenience we have also designated an interior fillet angle D which isincluded between the horizontal and the interior of the upper generallyfrusto-conical wall.

It will be apparent from a consideration of FIG. 2 that the sum of theangles A and B is equal to the angle D, being alternate interior angles.Still further, it will be apparent that the sum of the angles C and D isThe tanks generally employed in production today have an interior filletangle D of 45 and with a lower fillet angle A of about 10 to 15. Intesting the invention,-we first considered the bottom wall 14 and thelower frusto-conical sidewall 15. For good drainage to a circumferentialextraction plate surrounding the rotor we have determined that the angleA should not be less than about 15. We further have found thatincreasing the angle A is beneficial so to approximate optimum resultsselected an angle of 20 as not creating excesssive deflection to flowfrom the rotor 11 but at the same time providing good drainage. Wethereupon constructed three laboratory scale pulping tanks, each with abottom angle A of 20. The first test unit approximated the prior art (asoptimized) by having an interior fillet angle D of 45. The other twolaboratory tanks had fillet angles D of 55. The second of the tanks hadthe fillets so arra ged that the heights of the two frusto-conicalsidewalls l and 16 (as designated h, and 11 in FIG. 2) approximatelyequal. In the third case the height I1 was approximately twice the valueof 11,;

The tests were run using printed news material repulped to standardizedcondition with a consistency of 4% and 5% on the air-dried basis.

In general, advantageous results were obtained in utilizing the largerinterior fillet angles (tanks 2 and 3.)-

over the tank with the smaller interior fillet angle (tank 1). Thedifference in results were even greater than comparing the smallinterior fillet angle tank (tank 1) with tank 3. Although themeasurement of surface stock rates varied considerably due touncontrollable physical variables of the fiber as well as temperatureand stability, the general trend of results indicate that the tank 3averaged 1 1% higher surface ratesthan tank 1. This circulation increaseappeared about the same with either the rotor of U.S. Pat. No. 2,858,990or the rotor of my above-identified application, Ser. No. 330,081 whenoperated in the range of 45% A.D consistency. It was also found that toproduce the same given level of surface circulation, thethird tankrequired approximately 6% less power as compared with the first tank.

At the normal rated stock level for each tank (2.132 cubic feet), therewas no significant change in direction of stock flow, either at thesurface or along the outer elevation, when a comparison was made atequal rotor speed, input power or surface rate. However, if rotor speedor input power was held constant and the stock level was lowered,surface circulation increased and the vortex was proportionally deepenedresulting in a tighter involute surface pattern, but not to the extentof exposing the rotor at a 25% reduction in capacity. Tank 3 showedbetter circulation at 25% increase in level than tanks 1 and 2, orconversely lower power at equal circulation rates.

The table below indicates the range of fillet angles which can beemployed advantageously in the practice of the invention.

A B C D 15 35 40 5O 15 37.5 37.5 52.5 20 30 4O 50 20 32.5 37.5 52.5 2035 35 55 25 3O 35 55 25 32.5 32.5 57.5 30 -30 30 60 From the foregoing,it is seen that no angle of deflection (A, B or C) should exceed 40 and,that in the direction of flow, the relationship of the deflectionangles, from lower to higher, should be equal or increasing, but neverdecreasing. At the same time, in order to achieve the advantageousresults of the invention, the height, 11 of the upper frusto-conicalwall 16 should be at least 50% larger than the height, h of the lowerfrusto-conical wall 15, but not greater than In other words, the rangeof the ratio 11 /11 is 1.5 to 2.5.

Although only a single-rotor embodiment has been illustrated, personsskilled in the art will readily appreciate that the invention could beincorporated into a double-rotor pulper of the type disclosed inco-owned U.S. Pat. No. 3,602,440, issued Aug. 31, 1971.

We claim:

1. A pulper tank having an upright, generally cylindrical sidewallspaced above a generally horizontal bottom wall of similar diameter thansaid cylindrical sidewall, a rotor mounted above said bottom wall andbelow said cylindrical sidewall, and at least two up.- wardly divergentgenerally frusto-conical walls, one above the other, coupling saidbottom wall with said cylindrical sidewall, the lower of saidfrusto-conical walls forming a first exterior angle in the range 20 25with the horizontal, a second exterior angle being that between theupper and lower frusto-conical walls and being at least equal to saidfirst angle, and in the range 30 35, a third exterior angle being thatbetween the upper frusto-conical wall and said upright cylindrical walland being at least equal to said second angle, and in the range 30 35,the ratio of the height of said upper frusto-conical wall to the heightof said lower frusto-conical wall being in the range of 2.5 to 1.5.

1. A pulper tank having an upright, generally cylindrical sidewallspaced above a generally horizontal bottom wall of similar diameter thansaid cylindrical sidewall, a rotor mounted above said bottom wall andbelow said cylindrical sidewall, and at least two upwardly divergentgenerally frusto-conical walls, one above the other, coupling saidbottom wall with said cylindrical sidewall, the lower of saidfrusto-conical walls forming a first exterior angle in the range 20* -25* with the horizontal, a second exterior angle being that between theupper and lower frusto-conical walls and being at least equal tO saidfirst angle, and in the range 30* - 35*, a third exterior angle beingthat between the upper frusto-conical wall and said upright cylindricalwall and being at least equal to said second angle, and in the range30* - 35*, the ratio of the height of said upper frusto-conical wall tothe height of said lower frusto-conical wall being in the range of 2.5to 1.5.